A number of papers have been published which describe the requirements for laboratory cultivation of snail intermediate hosts (Biomphalaria sp., Bulinus sp., Oncomelania sp., and Tricula sp.) and their corresponding schistosome species (Schistosoma mansoni, S. heamatobium., S. japonicum, an S. mekongi) in sufficient numbers to support simultaneous programs in chemotherapy, immunology, physiology, pathology and other areas of biomedical research. Certain optimal physical conditions are necessary for the successful cultivation of snails. These are pH, oxygen content, water free of chlorine, copper, zinc and other harmful trace metals, temperature, absence of harmful protozoans and metazoans, and regular removal of decayed food and other debris from the culture aquaria. These physical environmental conditions are given high priority by persons involved in the maintenance of snails in the laboratory. During the past twelve years through ongoing National Institutes of Health contract, several new snail cultivation and maintenance units as well as some cost efficient new techniques such as snail exposures, detection of infection, detection and cercarial shedding, designed for large scale operation have been developed. These improvements are included in this proposal.